Tube DIY Asylum

Push Pull using 6n14n in place of EL84's/6BQ5's

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slownlo

A

I have some Russian 6n14n (6P14P) I'd like to use for a push pull amp project...I'll be using a pair of Edcor 10K PP trans with 40% screen taps...I attached the Bruce Heran (ODDWATT) schematic below...I'm curious about the design because it uses a CCS on the cathodes of the output tubes. Bruce calls it a "common cathode impedance, self balancing inverter"...

My question is about the use of the Russian 6n14n's IPO of the 6BQ5's...is there a siginificant difference in the tubes? Will using 10K primary negatively impact the performance?

Follow Ups:

RE: Push Pull using 6n14n in place of EL84's/6BQ5's - Eli Duttman 17:24:53 12/19/09 (4)
The Russian 6П14П is electrically equivalent to the 6BQ5/EL84, but its tonal reputation is far from sterling. OTOH, the 6П14П-EB is a genuine 7189 equivalent, with decent, if unspectacular, sonics.

Frankly, I have grave doubts about any ultralinear mode circuit that does not employ loop NFB of some kind. The damping factor will be too low. :> ( Also, combining splitter and "finals" in a single stage halves the gain the stage can yield. That's (IMO) not good.

Eli D.
- RE: Push Pull using 6n14n in place of EL84's/6BQ5's - Jim McShane 11:43:47 12/20/09 (0)
  Just a brief thought - I think Eli is understating the sonic qualities of the 6P14P-EB tube a bit. I think they are pretty good tubes - no, not Mullards or Genalex reissues - but quite nice tonally. Excellent bass is one of the strong points too.
  If Eli meant the 6P14P (not the EB) then I totally agree.
  His points on the circuit are well taken - both this post and the others.
  
  Edits: 12/20/09
- RE: Push Pull using 6n14n in place of EL84's/6BQ5's - slownlo 19:12:36 12/19/09 (2)
  Is this known as the "Schmitt Phase Inverter"...?
  1/2 gain yeild seems to be a compromise of the design in favor of balance...?
  - RE: Push Pull using 6n14n in place of EL84's/6BQ5's - Eli Duttman 20:08:10 12/19/09 (1)
    Schmitt, cathode coupled, and LTP are names used for variations on the differential gain block theme. That's 3 names for what is, for all intents and purposes, the same topology.
    
    The circuit you posted constructs the differential gain block out of the O/P tubes. IMO, you would do better with differential topology in both the driver and O/P stages. Allen Wright is big on forced symmetry (tail CCS) for splitter and "finals". The "drawback" to the scheme is only Class "A" operation is possible.
    
    BTW, the 12AU7 shown in the schematic has problems in the linearity dept. Changing type to a 6FQ7 deals with linearity and requires no parts value changes. JMO, restrict the 'U7 to cathode follower and "concertina" phase splitter duty.
    
    Eli D.
    - RE: Push Pull using 6n14n in place of EL84's/6BQ5's - slownlo 11:21:39 12/20/09 (0)
      Thanks Eli...

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